While standing still, Streamer gains 3% of the materials that they're holding as income, each second. So if you have 100 materials, you'll get 3 materials each second while standing still. This has a minimum of 1 material per second, and a maximum of 25 per seconds. It takes 834 materials to reach the maximum +25 materials per second.
The timer for 'standing still' resets each time you move, so you always need to stand still for a full second before you make any money.
While you can earn a lot of money this way, be careful as the negative penalties to % damage and Speed also increase. You can find yourself dealing very little damage, or moving very slowly towards the end of a wave. This can end your run easily. So keep your greed in check and stand still responsibly.